To improve fuel economy automotive air conditioning systems control compressor operation to avoid unnecessary cooling and to avoid icing the evaporator. The clutch between the engine and the compressor is controlled by either a thermostatic switch or a pressure switch with the pressure switch having cost and installation advantages. Use of the pressure switch has been confined to flooded evaporator type systems where the pressure changes slowly. In a finned coil evaporator, the pressure changes rapidly when the compressor starts and a pressure switch causes the clutch to cycle too fast. Therefore, finned coil systems have used the less desireable thermostatic switch.